Electrostatic discharge countermeasure for docking cradles with exposed pins that connect to an active interface

ABSTRACT

Apparatus and methods for disabling a USB or other interface connection between a personal computer and a docking cradle or device until the instant such a connection is actually needed. When the docking cradle is empty, the exposed pins are connected to a conductive ground path or is isolated. When a device is inserted into the docking cradle, the electrical signals that are connected to the personal computer by way of the interface are then switched on.

TECHNICAL FIELD

The present invention relates generally to electrostatic dischargeevents in portable electronic devices, and more specifically, toimproved electrostatic discharge countermeasure for docking cradleshaving exposed pins that connect to an active USB interface.

BACKGROUND

Portable electronic devices such as digital cameras, laptop computers,handheld personal digital assistants (PDA's), and the like, are oftensold with docking stations or docking cradles. These docking devices aregenerally connected to a host device, usually a personal computer.Often, the host device and the docking device are connected by commoninterface cables and protocols, such as a Universal Serial Bus (USB)interface. In order to maintain portability and ease of use, the deviceto be docked (i.e.,. camera) must interface with an input-outputconnector on the docking cradle. The nature of the docking cradleinput-output connector is often such that the pins are exposed toelectrostatic discharge (ESD) events.

When an ESD event occurs on an input-output pin that is connected to apersonal computer, the ESD voltage discharge can propagate through thedocking cradle to the personal computer. ESD events can result in dataloss, unwanted personal computer user intervention, and sometimesphysical damage of the personal computer's internal electronic hardware.

The ESD event frequently poses its primary risk when there is no devicein the docking station. That is, after the dockable device is insertedinto a docking station, the input-output pins are no longer exposed, andno further direct threat exists.

There are many examples of conventional methods that prevent unwantedESD discharge to this type of docking station device. Other methods ofprotecting a product from high levels of ESD may require the addition ofadditional ESD suppression components such as diodes, Zener diodes,resistors and capacitors. These components are sometimes costly, andthey are subject to failure after being exposed to a large number ofcycles. The number of cycles before failure is also a function of theapplied voltage and resulting current. Also, the addition of typical ESDsuppression devices may have the highly undesirable effect of decreasingthe quality of the USB signal.

U.S. Pat. No. 6,089,879 discloses a “dual-in-line Universal Serial Bus(USB) connector including a plurality of USB ports, a plurality ofsignal pins associated with the ports, and a pair of mounting tabs. TheUSB connector is adapted for a circuit board including a first footprintfor the dual-in-line USB connector situated at a predetermined locationof the circuit board. Also, a second footprint is situated at apredetermined location of the circuit board for receipt of a differenttype of connector instead of the USB connector.”

U.S. Pat. No. 6,178,514 discloses “an apparatus and method forinterfacing a bus to a device. The bus includes a power line carryingpower and a signal line carrying a signal. The device including a powerinput and a signal input. The interface includes a power outputconnected to the device power input; a power input connected to the buspower line; a signal input connected to the bus signal line; a signaloutput connected to the device signal input; an energy storage devicehaving an input and an output, the energy storage device outputconnected to the interface apparatus power output; and a power converterhaving a power input connected to the interface apparatus power inputand a power output connected to the energy storage device input, wherebythe power converter receives power from the bus power line and convertsit to a form suitable for charging the energy storage device. The powerconverter further includes a current sensor and a current limiter. Thecurrent sensor is connected in series with the power converter powerinput and output and has an output carrying a signal representative ofthe current flowing through the current sensor. The current limiter hasa predetermined current limit and is operably connected to the powerconverter power input and power output. The current limiter also has aninput connected to the current sensor output for receiving the currentsensor signal representative of the current flowing through the currentsensor, whereby the current limiter limits the current drawn by thedevice and the interface apparatus to the predetermined current limit.The interface also includes a signal conditioner that has a first inputconnected to the energy storage device output, a second input connectedto interface apparatus signal input or the interface apparatus signaloutput, and an output connected to the interface apparatus signaloutput. The signal conditioner includes a transfer function thatproduces a signal conditioner output signal at the signal conditioneroutput. This transfer function is a function of the level of energy inthe energy storage device and the level of energy of the bus signal orthe signal conditioner output signal.”

U.S. Pat. No. 6,205,505 discloses a “universal serial bus (USB)transmission system for transmitting a monitor control signal and a datasignal from a monitor system to a main frame is provided. The universalserial bus transmission system separately includes a universal serialbus interface IC and a monitor controller IC between which the monitorcontrol signal and the data signal are transmitted through a low-speedtransmission interface, thereby reducing costs for handlingelectromagnetic interference (EMI). Furthermore, the universal serialbus interface can be modularized to allow the monitor system to serve asa general monitor system or a USB monitor system, thereby increasing theutility of the monitor system.”

U.S. Pat. No. 6,210,216 discloses that a “USB (Universal Serial Bus)cable includes a cable having an end to which a connection device isattached. The connection device includes an insulative casing in whichtwo USB connectors are fixed and electrically connected to the cable.Two bores are defined in a front wall of the casing for rotatablyretaining two bolts. A conductive plate associated with each bolt isfixed in the casing having a first section defining a hole through whichthe bolt extends and a second section resiliently engaging with aconductive shield of the corresponding USB connector. The first sectionhas step-like edges fixedly received in L-shaped slits defined in thefront wall with the first section overlapping an outside surface of thefront wall whereby when the connection device is secured to an externalgrounding panel by the bolts, the conductive plate engages with thegrounding panel forming an electrical connection between the shield ofthe corresponding USB connector and the grounding panel.”

U.S. Pat. No. 6,241,537 discloses “a handheld computer includingelectrostatic discharge feature. The electrostatic discharge feature isconfigured on the connector of the handheld computer to dissipate anelectrostatic charge having a voltage exceeding a threshold level uponthe connector being made with another connector of an accessory device.Examples of an accessory device include communication cradles for usewith handheld computers. U.S. Pat. No. 6,241,537 also discloses that“embodiments of the invention provide a versatile connector with acurrent path to dissipate charge delivered by an ESD event. This featureincludes potential damage from ESD events particularly during andconnection and deconnection to an accessory device. Further, embodimentsof the invention improve reliability in making and maintaining anelectrical connection between the handheld computer and accessorydevice. Additionally, the current associated with an ESD event and itsderivative are reduced, minimizing damage such as latchups, registererasure, data loss and physical damage.”

U.S. Pat. No. 6,315,609 discloses an “improved structure universalserial bus (USB) connector female socket in which a grounding ring isdisposed at the lower edge of a metal housing enclosing the connectorterminals, with the two sides of the metal housing covered by aninsulative integument to form the USB connector female socket. Thegrounding ring can be fastened by a screw and, furthermore, the metalconstruction of the grounding ring strengthens signal transmission,while also providing for grounding capability, thereby enabling thepresent invention to strengthen bidirectional signal transmission aswell as effectively prevent the occurrence of electrostatic discharge(ESD) during computer peripheral (such as scanners, digital cameras, andkeyboards, etc.) operation.”

U.S. Pat. No. 6,347,948 discloses “a cable connector assembly includes apair of USB connectors, a cable end connecting to the pair of USBconnectors, a pair of conductive latches positioned at either side ofthe USB connectors, a cover enclosing the USB connectors, and groundingbars positioned on an outer surface of the cover. Each latch is V-shapedand has a first arm electrically engaging with a shrouded shell of thecorresponding USB connector, and a second arm extending out from thecover to electrically and mechanically engage with a grounded panel ofan electronic apparatus with which the cable connector mates. Eachgrounding bar has a base portion located on the cover and a pair ofconductive tabs extending from the base portion into the cover andelectrically engaging with the shrouded shells of the pair of USBconnectors. The base portion of each grounding bar forms a pair ofspring fingers extending forwardly therefrom. When the cable connectoris mated with the electronic apparatus, the pair of latches engage withthe grounded panel of the electronic apparatus and free ends of thespring fingers of the grounding bar press against the panel, therebyestablishing electrical connection between the shrouded shells of theUSB connectors and the grounded panel of the electronic apparatus.”

U.S. Pat. No. 6,364,699 discloses “a cable connector assembly and ashroud partially covering the cable connector assembly. The shroud isslidable in a rear-to-front direction over the cable connector assembly.The cable connector assembly includes a pair of USB connectors, a cableend connecting to the pair of USB connectors, a pair of conductivelatches positioned at either side of the USB connectors, a coverenclosing the USB connectors and the cable end at front and rearportions thereof, and grounding bars positioned on outer surfaces of thecover. Each latch is V-shaped and has a first arm electrically engagingwith a shrouded shell of the corresponding USB connector, and a secondarm extending out from the cover to electrically and mechanicals engagewith a grounded panel of an electronic apparatus with which the cableconnector assembly mates. Each grounding bar has a base portion locatedon the cover and a pair of conductive tabs extending from the baseportion into the cover and electrically engaging with the shroudedshells of the pair of USB connectors. The base portion of each groundingbar forms a pair of spring fingers extending forwardly therefrom. Whenthe cable connector assembly device is mated with the electronicapparatus, the pair of latches engage with the grounded panel of theelectronic apparatus and the shroud is moved in the rear-to-frontdirection over the cable connector assembly, allowing circular lips ofthe shroud to abut against a portion of each latch to prevent thelatches from disengaging from the grounded panel. Further, front freeends of the spring fingers of the grounding bars press against thegrounded panel, thereby establishing further electrical connectionbetween the shrouded shells of the USB connectors and the grounded panelof the electronic apparatus.”

U.S. Pat. No. 6,382,997 discloses “a connector having a groundingelement and a housing of an electrically insulating material. Thehousing includes at least one contact element comprising a contact end,an intermediate part, and a connection end. The connector also includesan electrically insulating voltage variable medium that is providedbetween the at least one contact element and the grounding element. Theelectrically insulating voltage variable medium becomes electricallyconducting at a voltage that is substantially higher than the operatingvoltages of a device for which the connector is intended or of which itis a part. The connector described herein is relatively compact andenables constant ESD suppression.”

U.S. Pat. No. 6,424,525 discloses “a system that enables a plurality ofexternal peripheral devices to be easily connected to a conventionalpersonal computer, or other computing device. The system can include thecomputer, or can alternatively be configured as a hub. In eitherconfiguration, the system includes an arcuate-shaped interface surface,on a base. One end of the interface surface includes an upright chassis,which includes a plurality of bays. Rails extend longitudinally alongthe interface surface, toward each bay. An external peripheral device isslid over a rail, which provides attachment and stability to the deviceand aligns it with the bay. Each bay includes an alignment pin, a powerconnection, and a data connection. Adjacent to each rail is a latch forsecuring an external peripheral device in a bay. The top of the chassisincludes a marking to provide a visual reference that aids in attachingan external peripheral device to a bay. The rails can provide anelectrical ground and/or include an element that provides electro-staticdischarge protection. In one embodiment, the rails are configured toprovide electrical contact for coupling power into a peripheral device,and/or coupling to a data port on an external peripheral device.”

U.S. Patent Application 2002/0024791 discloses that an “electricalcircuit protection device has an overcurrent protection portion and anovervoltage protection portion. The overcurrent protection portion has asurface. The overvoltage protection portion is disposed on the surface.In one preferred embodiment, the overcurrent portion includes a PTCdevice and the overvoltage portion includes a voltage variable material.A number of terminations are configured to connect the overcurrentprotection portion and the overvoltage protection portion to a printedcircuit board.”

U.S. Patent Application 2001/0046801 discloses that an “embodiment ofthe invention includes a handheld computer including electrostaticdischarge feature. The electrostatic discharge feature is configured onthe connector of the handheld computer to dissipate an electrostaticcharge having a voltage exceeding a threshold level upon the connectorbeing made with another connector of an accessory device. Examples of anaccessory device include communication cradles for use with handheldcomputers.” U.S. Patent Application 2001/0046801 also discloses that“Among other advantages, embodiments of the invention provide aversatile connector with a current path to dissipate charge delivered byan ESD event. This feature includes potential damage from ESD eventsparticularly during and connection and de-connection to an accessorydevice. Further, embodiments of the invention improve reliability inmaking and maintaining an electrical connection between the handheldcomputer and accessory device. Additionally, the current associated withan ESD event and its derivative are reduced, minimizing damage such aslatchups, register erasure, data loss and physical damage.”

However, none of the above-cited patents or patent applications discloseor suggest apparatus or methods for providing electrostatic dischargeprotection for a docking station wherein, when there is no dockabledevice in the docking station the signal lines of the USB interface areconnected to ground, and when the dockable device is docked with thedocking station the signal lines of the USB interface are removed fromconnection to ground.

It is an objective of the present invention to provide for an apparatusand method that provides electrostatic discharge countermeasures fordocking cradles having exposed pins that connect to an active USBinterface.

SUMMARY OF THE INVENTION

To accomplish the above and other objectives, the present inventionprovides for apparatus and methods for disabling an active interface,such as a USB interface or connection, for example, between a personal(host) computer and a docking station or cradle until the instant such aconnection is actually needed. Exemplary embodiments of the presentapparatus and methods provide for a dockable device having a dockingconnector, docking station having an actuator for detecting the presenceof the dockable device and having an input-output connector that mateswith the docking connector of the dockable device, and a host computercoupled to the docking station by way of an interface.

In accordance with the present invention, the actuator connects signallines of the interface to ground when there is no dockable device in thedocking station, and the actuator removes the signal lines of theinterface from connection to ground when the dockable device is dockedwith the docking station. Thus, when the docking cradle is empty, theexposed pins are connected to a conductive ground path or are isolated.When a device is inserted into the docking cradle, the electricalsignals that are connected to the personal computer by way of the USBinterface are then switched on.

In contrast to conventional methods, the present invention is not likelyto experience any degradation if exposed to a very large quantity of ESDevents of high voltage. In addition, the present invention should notmaterially impact the quality of the USB signal while providing ESDprotection.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of embodiments of the presentinvention may be more readily understood with reference to the followingdetailed description taken in conjunction with the accompanyingdrawings, wherein like reference numerals designate like structuralelements, and in which:

FIG. 1 illustrates an exemplary system in accordance with the principlesof the present invention;

FIG. 2 shows an exemplary wiring diagram used in the system shown inFIG. 1; and

FIG. 3 illustrates an exemplary method in accordance with the principlesof the present invention.

DETAILED DESCRIPTION

Referring to the sole drawing figures, FIG. 1 illustrates an exemplarysystem 10 in accordance with the principles of the present invention.The exemplary system 10 shown in FIG. 1 illustrates a typicalconfiguration of a docking station 12 or cradle 12 having an actuator 14for detecting the presence of a dockable device 11 (camera 11), and aninput-output connector 13. The dockable device 11 has a dockingconnector 11 a that mates with the input-output connector 13 which formuniversal serial bus (USB) connector 17. The docking station is coupledto a host computer 16 by way of a universal serial bus (USB) interface15 and interface cable.

FIG. 2 shows an exemplary wiring diagram of the docking station 12 shownin FIG. 1. FIG. 2 illustrates the configuration of USB communicationlines (USB+, USB−) of the USB interface 15 and how their configurationchanges in response to activation of the actuator 14 of the dockingstation 12.

With the docking station 12 connected to the host computer 16, the USBsignal lines USB+, USB− (that are exposed in the input-output connector13 of the docking station 12, are intentionally connected electricallyto ground by way of the actuator 14, which may comprise a mechanical orelectronic switch 14. If an ESD event occurs on an exposed pin of theinput-output connector 13, the charge is dissipated directly to groundby way of the mechanical or electronic switch 14 comprising the actuator14.

When the camera 11, a personal digital assistant (PDA) 11, or otherdockable device 11, is inserted into the docking station 12 or cradle12, the switch 14 (actuator) is latched, which then disconnects the USBlines USB+, USB− from ground and re-establishes their connection to thedocking input-output connector 13. Since the dockable device 11 orcamera 11 is now in the docking station 12 or cradle 12, the previously“exposed” pins of the input-output connector 13 are now shielded fromfuture direct ESD discharges.

When the dockable device 11 or camera 11 is removed from the dockingstation 12 or cradle 12, the actuator 14 of the docking station 12 orcradle 12 returns to its previous condition, and again connects theexposed pins of the input-output connector 13 to ground and thus guardsagainst future ESD events.

A mechanical actuator 14 on the docking station 12 serves to detect thepresence of the dockable device 11 or camera 11 on the docking station12. This function may also be replaced by an electronic switch 14 thatresponds to the condition of the dockable device 11 or camera 11 when itis “docked” as opposed to when it is “not docked.”

For the purposes of completeness, FIG. 3 illustrates an exemplary method30 in accordance with the principles of the present invention forproviding electrostatic discharge countermeasures in a dockable device11. The exemplary method 30 comprises the following steps.

A dockable device 11 having a docking connector 11 a is provided 31. Adocking station 12 having an input-output connector 13 and an actuator14 for detecting the presence of the dockable device 11 is provided 32.The docking station 12 is coupled 33 to a host computer 16 by way of aUSB interface 15. When there is no dockable device 11 in the dockingstation 12, signal lines of the USB interface 15 are connected to ground34. When the dockable device 11 is docked with the docking station 12,the signal lines of the USB interface 15 are removed from connection toground.

Some advantages of using the present invention to control high levels ofESD are that it eliminates the need to add ESD suppression devices alongcommunication signal lines (i.e., the USB signal lines). The relativesignal quality on the USB lines is important for proper devicefunctionality, and its quality is generally degraded when ESD devices(diodes, for example) are present. The use of the present invention thusavoids signal quality degradation resulting from ESD-protection-relatedissues. The use of the actuator 14 or switch 14 may also consume lessphysical space than a configuration of conventionally-used Zener diodesor other ESD suppression devices.

Conventional techniques for protecting a product from high levels of ESDmay require the addition of additional ESD suppression components suchas diodes, Zener diodes, resistors and capacitors. The present inventioneliminates the need for these other devices by creating a direct groundpath for ESD discharges when the pins are exposed by the absence of thedockable device 22 (such as the camera 11).

Thus, improved apparatus and methods that provide electrostaticdischarge countermeasures for docking cradles having exposed pins thatconnect to an active USB device have been disclosed. It is to beunderstood that the above-described embodiments are merely illustrativeof some of the many specific embodiments that represent applications ofthe principles of the present invention. Clearly, numerous and otherarrangements can be readily devised by those skilled in the art withoutdeparting from the scope of the invention.

What is claimed is:
 1. Apparatus comprising: a dockable device having adocking connector; a docking station having an actuator for detectingthe presence of the dockable device and having an input-output connectorthat mates with the docking connector of the dockable device; and a hostcomputer coupled to the docking station by way of an interface; andwherein the actuator connects signal lines of the interface to groundwhen there is no dockable device in the docking station, and wherein theactuator removes the signal lines of the interface connection fromground when the dockable device is docked with the docking station. 2.The apparatus recited in claim 1 wherein the dockable device comprises acamera.
 3. The apparatus recited in claim 1 wherein the dockable devicecomprises a personal digital assistant.
 4. The apparatus recited inclaim 1 wherein the actuator comprises a mechanical actuator.
 5. Theapparatus recited in claim 1 wherein the actuator comprises anelectronic actuator.
 6. The apparatus recited in claim 1 wherein theinterface comprises a USB interface.
 7. A method of providingelectrostatic discharge countermeasures for a dockable device,comprising the steps of: providing a dockable device having a dockingconnector; providing a docking station having an input-output connectorand an actuator for detecting the presence of the dockable device;coupling the docking station to a host computer by way of an interface;when there is no dockable device in the docking station, connectingsignal lines of the interface to ground; and when the dockable device isdocked with the docking station, removing the signal lines of theinterface from connection to ground.
 8. The method recited in claim 7wherein the dockable device comprises a camera.
 9. The method recited inclaim 7 wherein the wherein the dockable device comprises a personaldigital assistant.
 10. The method recited in claim 7 wherein the whereinthe actuator comprises a mechanical actuator.
 11. The method recited inclaim 7 wherein the wherein the actuator comprises an electronicactuator.
 12. The method (recited in claim 7 wherein the interface ischaracterized by a USB interface.